Age and Origin of the Massangana Intrusive Suite and Associated Mineralizations, in the Rondônia Tin Province: Petrography, U-Pb, and Lu-Hf Isotopes Zircons

Abstract

Rondônia intrusive suites represent the youngest A-type magmatism that occurred in the SW of the Amazon craton, with mineralizations in Sn, Nb, Ta, W, and topaz. Petrological and isotopic studies (U-Pb and Lu-Hf by LA-ICP-MS) allowed the Massangana granite to be subdivided into São Domingos facies (medium to fine biotite-granite), Bom Jardim facies (fine granite), Massangana facies (pyterlites and coarse granites) and Taboca facies (fine granites). The crystallization ages obtained were between 995.7 ± 9.5 Ma to 1026 ± 16 Ma, and the εHf values vary significantly between positive and negative, showing predominantly crustal sources for forming these rocks. Petrographic studies on ore samples indicate the action of co-magmatic hydrothermal fluids enriched in CO2, H2O, and F. These ores are characterized by endogreisens, exogreisens, pegmatites, and quartz veins that are explored in the São Domingos facies area. The endogreisens and exogreisens are formed by topaz-granites and zinnwaldite-granites; the pegmatites are formed by topaz-zinnwaldite-cassiterite-granites; and the veins by cassiterite-sulfides and quartz. The geometries of the mineralized bodies indicate a dome-shaped contact with the host rocks in the magma chamber and can be attributed to residual accumulation. In this sense, the origin of these ores is related to the evolution of intrusive granitic bodies where the terminal phases of the fluid-enriched magma are lodged in the apical portions, and the origin of the mineralized bodies present a biotite-granite, albite-granite, and endogreisens evolution (potassium series), or biotite-granite, alkali-granite and endogreisens (sodic series) and these rocks present TDM ages that indicate a concerning relation to the non-mineralized rocks of Massangana granite.